1. Field of the Invention (Technical Field)
The present invention relates to creating and automatically identifying synthetic aperture radar images.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Synthetic Aperture Radar (SAR) images are two-dimensional (2D) projections of scattering centers from a three-dimensional (3D) target. Use of such images in automated target detection and classification is known, as described in, for example, MedI and Hughen, “Application of SAR Fundamental Angles to ISAR and Moving Target Imaging Problems”, Algorithms for Synthetic Aperture Radar Imagery XI, SPIE Defense and Security Symposium, Orlando, Fla., 2004; MedI and Hughen, “New Explanation of Relative Motion in ISAR and Moving Target Imaging Problems from a Target-centric Viewpoint Using SAR Fundamental Angles”, Algorithms for Synthetic Aperture Radar Imagery XI, SPIE Defense and Security Symposium, Orlando, Fla., 2004; Kim, Pergande, and Hughen, “Low Cost Ka Band SAR/ISAR for UAV Applications”, IEEE Aerospace Conference Proceedings, 2003; and Jakowatz, et. al., Spotlight-mode Synthetic Aperture Radar: A Signal Processing Approach, Kluwar Academic Publishers, Norwell, Mass., 1996.
When a highly maneuverable vehicle, such as an unmanned aerospace vehicle (UAV) or a missile, is used to create the SAR image, it is possible to obtain “tilt angle diversity” on a target. In other words, multiple SAR images can be taken of a vehicle, each one having a different 2D projection of the 3D target. In the prior art such tilt angle diversity is considered an obstacle to correct target classification. However, the present invention uses this diversity as an aid to correct target classification.
With the present invention, each image can be identified individually and decisions can be fused together by post-processing algorithms. This process increases the probability of correct identification/classification of a target by fusing multiple decisions together from diverse SAR images. The tilt angle is one angle that describes the intersection of the SAR projection plane (i.e., slant plane or range-doppler plane) with the target body. For applications such as range-doppler imaging, having tilt angle diversity has been considered a problem or a nuisance. It has not heretofore been considered that tilt angle diversity could be beneficially employed.
The present invention employing tilt angle diversity increases the probability of correct identification/classification (Pcc) of the target as against a single image. If the Pcc of a “single look” is lowered in the “multilook” system of the present invention, it becomes possible to relax the cross-range resolution requirements, thus decreasing the single look integration time and the CPU memory and throughput requirements of the image formation processor (computer hardware executing software embodying the invention). The signal-to-noise (SNR) ratio of the system could also be lowered, permitting a lower powered, cheaper, and lighter radar system component of the invention.